1,317 research outputs found
The rheological behaviour of suspensions of fat particles in oil interpreted in terms of a transient-network model
The transient-network model for concentrated dispersions, described in a previous paper, is used to describe the rheological behaviour of dispersions of glyceryl tristearate crystals in paraffin oil. The model prediction of the storage modulus of this system is compared with corresponding expressions given in literature. Model calculations are carried out to fit the linear viscoelastic behaviour of the system as well as its stress response in large amplitude shear experiments. Information is thus obtained about the stiffness and strength of the interparticle bonds, and the chance of them breaking in a state of rest or as the result of flow. It is concluded that the probability of interparticle bond fracture strongly depends on the measure of bond stretching. The general findings link up with the Lennard-Jones potential which is assumed to describe the potential energy of the bonds between the particles. Accurate measurements of the temperature dependence of the dynamic moduli by making use of a torsion resonator lead to the conclusion that the energy dissipation at a high frequency originates mainly from the flow of liquid around the particles
A transient-network model describing the rheological behaviour of concentrated dispersions
Attractive forces acting between particles in dispersions may cause a three-dimensional structure to be built up. A temporary-network model is postulated that describes the rheological behaviour of such systems. Chains of particles are assumed to be created and broken by thermal actions and by applied deformation. The relation between the network structure and the macroscopic stress tensor is deduced. One of the main model features is that no use is made of the common assumption of affinity of the motion of the chain vectors with the gradient of the macroscopic velocity field. Instead, the chain deformations are assumed to depend on the forces acting on them, i.e. their deformations depend on their stiffness and on the applied deformation, whereas fracture of chains may cause stress relaxation in the rest of the network. The chains may behave as highly non-linear springs, whereas the probability that the chains will break in some time interval may be an explicit function of the chain length itself. Integral equations are derived, from which the stress-tensor components can be calculated in any flow experiment, that obeys creeping-flow conditions. Analytical expressions are obtained for the relaxation spectrum of such systems in terms of the microscopic parameters
Post-Combustion CO2 capture using supported amine sorbents: A process integration study
We have evaluated the feasibility of supported amine sorbents (SAS) for their application in post- combustion CO2 capture. For this, the energy efficiency of a power plant equipped with a supported amine based capture facility is compared with the energy efficiency of a power plant equipped with a standard MEA-capture facility using the Spence®software tool developed by DNV-KEMA. Based on the simulations performed, application of a SAS-based capture facility at a natural gas combined-cycle (NGCC) plant is potentially 19% more energy efficient than a MEA-capture facility. For a pulverized- coal (PC) plant, the SAS-based plant could save up to 32% of the energy required in the MEA proces
The squeezing of liquid out of a structured dispersion
The equations predicting the rate of liquid removal out of a structured dispersion that is unilaterally compressed are presented in a nondimensional form. The dispersed particles, mostly solid and of colloidal dimensions, are assumed to compose a transient three-dimensional network. This letter refers to a previous paper in which the original equations, i.e., without being non-dimensionalized, were applied to calculate the rate of oil removal out of a dispersion of fat partciles under unilateral compression
The relation between the permeability of structured dispersions and the viscoelastic properties of the dispersed phase
It is shown that not only the average particle size and compression modulus, but also the viscoelastic properties of the network affect the rate of liquid removal out of a concentrated disperse system that is unilaterally compressed. A Maxwell-like constitutive equation is introduced to express these viscoelastic properties. The rate of liquid removal is calculated for a set of values of the elastic modulus and the time constant that appear in the constitutive equation. It is shown that permeability measurements on concentrated fat dispersions can be interpreted in terms of network properties also when the network is viscoelastic, i.e., it is assumed that processes take place inside the network that involve energy dissipation
Clinical Utility of the MMPI-2-RF Hierarchical Description:An Illustration in Cluster C Personality Disorder Patients
Several studies have addressed the associations between the Minnesota Multiphasic Personality Inventory-2 Restructured form (MMPI-2-RF; Ben-Porath & Tellegen, 2008) scale scores and the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association, 2013) Section II personality disorder (PD) criterion counts. While these studies showed which variables were associated with the PDs as well as their combined predictive potency, no information is available on mean patterns of elevation associated with these conditions. To illustrate how the MMPI-2-RF information may amplify categorical diagnostic information, we describe the mean RF profiles of a psychiatric sample with a Cluster C PD diagnosis. PD classification was based on the Structured Clinical Interview for the DSM-IV (SCID-II). Patterns of elevation across the three levels of the MMPI-2-RF scale sets were consistently in line with theoretical expectation. In addition, elevated scores on somatic/cognitive scales were noted. It is concluded that the MMPI-2-RF can enhance DSM Personality disorder model description.</p
Simple Models for Turbulent Self-Regulation in Galaxy Disks
We propose that turbulent heating, wave pressure and gas exchanges between
different regions of disks play a dominant role in determining the preferred,
quasi-equilibrium, self-similar states of gas disks on large-scales. We present
simple families of analytic, thermohydrodynamic models for these global states,
which include terms for turbulent pressure and Reynolds stresses. Star
formation rates, phase balances, and hydrodynamic forces are all tightly
coupled and balanced. The models have stratified radial flows, with the cold
gas slowly flowing inward in the midplane of the disk, and with the warm/hot
phases that surround the midplane flowing outward.
The models suggest a number of results that are in accord with observation,
as well as some novel predictions, including the following. 1) The large-scale
gas density and thermal phase distributions in galaxy disks can be explained as
the result of turbulent heating and spatial couplings. 2) The turbulent
pressures and stresses that drive radial outflows in the warm gas also allow a
reduced circular velocity there. This effect was observed by Swaters, Sancisi
and van der Hulst in NGC 891, a particularly turbulent edge-on disk. The models
predict that the effect should be universal in such disks. 3) They suggest that
a star formation rate like the phenomenological Schmidt Law is the natural
result of global thermohydrodynamical balance, and may not obtain in disks far
from equilibrium. (Abridged)Comment: 37 pages, 1 gif figure, accepted for publication in the Astrophysical
Journa
Agriculture and water in Shunyi District, Beijing; results of a rapid diagnostic appraisal
Land use and agriculture in Shunyi District were studied in a Rapid Diagnostic Appraisal (RDA) held November 2003 in the frame of the project `Resource Management Options in the Greater Beijing Area`. Officials of governmental institutions in Shunyi were interviewed and during three days, a team of nine Chinese and three Dutch researchers visited three townships in Shunyi District and interviewed local leaders and farmers on farm structures, farming systems, water-related issues and future developments. In addition, documentation and statistics about land use development and agriculture in Shunyi have been collected. The results of this rapid diagnosis have been presented during a feedback meeting with a major part of the interviewed officials and farmers. This report presents the results of the RDA. After a general description of land and water use developments in Shunyi, the major characteristics of agriculture are described. Subsequently, the main characteristics of the visited townships and farms are summarized. More detailed information about the approach and organisation of the RDA can be found in Appendix 2 of this report
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